System cooling in the spotlight. What to increase/decrease?

Cooling the GPU and the power supply circuit

Do you know how many fans do you need and what speed they should run at to achieve the optimal cooling of your PC case? Is it better to induce positive pressure, negative pressure, or balanced airflow? Are four fans with less RPM more effective than two with more RPM? We can answer all these questions by providing you results of more than 70 tests which also include the monitoring of the heating of power supply circuit of CPU and GPU.

Introductions

Properly optimized system cooling should be essential for every computer. Inappropriate air circulation can cause, for example, lower frequencies and thus lower performance of your graphics card, system instability, shorter life of components, higher noise level (with PWM), and similar issues.

Of course, avoiding these negative effects of insufficient (or excessive) cooling configuration can be accomplished just by a good estimate. But to achieve the best results possible, you need an accurate idea of how a particular setting can affect the temperature of the components. For this purpose, we used Noctua NF-S12A ULN fans which are designed exclusively for system cooling. Thanks to the larger angle under which their vanes are bevelled, they have wider range of their airflow.

   

What and how we were testing

We used four fans in the tests to create various combinations that are commonly used in practice. We moved from one fan to all four. All tested configurations are listed in the summary table. The number in brackets refers to the ratio of input and output fans, the inputs being listed first. The 1 + 2 represents one input and two output fans. Each of the configurations was tested at three levels of noise intensity, from a very quiet running to one that you cannot ignore, but within meaningful limits.

We used laboratory power supplies to set the speed of fans and the noise level was captured by the Reed R8080 sound level meter. During the tests the fans were installed in a wind tunnel and at the same distance from the sensor of the noise meter, approximately 30 cm (you can see the layout in the title photo).

It is good to note that with the same flow the input fans are always a little louder than the output fans because they are pushing the air (sound) into the case, which is reflected in several directions. It starts to change with cases that have a grid with a dense sieve on the output. However, we all know that the spiral design is ideal because it creates no resistance to the flowing air. There are also many other differences among various cases that are affecting the results, so we tried to achieve the conditions that are almost identical to the ideal. Our tunnel has no excess perforations and is properly tight. The position of the motherboard was standard, vertical.

During the tests, we were monitoring the temperature of Core i7-5930K @ 4.2 GHz (1.15 V) processor with the cooler Scythe Fuma (7 V) and MSI GeForce GTX 1060 Gaming X graphics card with regulated fans (4.37 V). Temperatures that are also important are those of power supply circuit which is even more dependent on system cooling since it usually have only passive cooling. We placed one thermocouple in both the CPU’s MOSFETs heatsink and the GPU cooling plate.

We simulated the burn in IntelBurnTest (10 GB) and FurMark. The duration of every simulation was 20 minutes and each subsequent test was preceded by a cooling phase. The intake air temperature was 21 – 21.3 °C, ensured in our air-conditioned lab.

   

Do you know how many fans do you need and what speed they should run at to achieve the optimal cooling of your PC case? Is it better to induce positive pressure, negative pressure, or balanced airflow? Are four fans with less RPM more effective than two with more RPM? We can answer all these questions by providing you results of more than 70 tests which also include the monitoring of the heating of power supply circuit of CPU and GPU.

Cooling the CPU and the power supply circuit

Do you know how many fans do you need and what speed they should run at to achieve the optimal cooling of your PC case? Is it better to induce positive pressure, negative pressure, or balanced airflow? Are four fans with less RPM more effective than two with more RPM? We can answer all these questions by providing you results of more than 70 tests which also include the monitoring of the heating of power supply circuit of CPU and GPU.

Cooling the GPU and the power supply circuit

Do you know how many fans do you need and what speed they should run at to achieve the optimal cooling of your PC case? Is it better to induce positive pressure, negative pressure, or balanced airflow? Are four fans with less RPM more effective than two with more RPM? We can answer all these questions by providing you results of more than 70 tests which also include the monitoring of the heating of power supply circuit of CPU and GPU.

Tips resulting from tests

More fans adjusted to the same level of noise have proven to be more effective, there was no doubt about that. Let’s take a look at the results in the processor section first.

Four (2 + 2) against two (1 + 1) fans can mean the difference of up to 12 °C when cooling more powerful processors. Even at the lowest noise level, the results of four fans, in the vast majority of cases, are better than the more noisy modes with less fans. If only two fans are available, it is more reasonable to install them both for the outtake. With one at the front and the other at the rear, the results are significantly worse. Even worse than with only one fan for the outtake which can run at the same noise level with 60 rpm more.

Interesting are the results with three fans, where it bounces between positive and negative pressure. While at higher noise levels, the negative pressure seems like a better choice for optimal cooling of the processor part, but odds change with lower flow. At 31.5 dBA (~ 495 rpm), we noticed the difference of 3 °C in the favour of the positive pressure. On the other hand, if you want to concentrate on the graphics part, negative pressure is better. That said, there is no “best” configuration, just an optimal configuration for particular areas.

If you own a dedicated graphics card, the previously winning 2 + 2 configuration appears to be a bit worse choice than 1 + 2. This does not apply to the case of 36 dBA mode where a stronger forward pressure positively affects things. Otherwise the negative pressure is always more efficient. This claim can be confirmed also by the comparison of the 0 + 2 and 1 + 1 configurations. It might seem that the balanced flow will be more suitable, but it is not. Although the front fan blows on the circuit, more intense negative pressure is more effective, again. However, the differences are really small, only up to 2 °C. Therefore, if you have a more perforated case that easily gets dusty, you can induce the positive pressure too. But be careful about the CPU section.

The worst results were achieved with a lone fan, and the fact that it ran with the highest rpm in the tests changes nothing. However, it is still an extremely important part of any desktop PC and even at the lowest noise level, at 31.5 dBA, it performed its necessary role. After its removal, it was no longer possible to properly cool the 320 W configuration. The heat was rapidly accumulated in the closed case, and after 10 minutes the temperatures of the components reached critical levels and the processor started to throttle. So, even one low-speed fan is very important and it is usually enough for most office configurations.

TL; DR: For more powerful computers, four fans with balanced flow are the most effective solution and you do not have to worry about decreasing the rpm to the minimum. Three fans creating negative pressure will do almost just as fine. In modern PC configurations without a dedicated graphics card and without any HDDs, the front fans do not play an important role and they help the system cooling only cosmetically. So, two fans for the outtake are enough.

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• Contents
• Introductions and test procedures
• Cooling the CPU and the power supply circuit
• Cooling the GPU and the power supply circuit
• Tips resulting from tests